Images are tagged during data processing to indicate specific types of conditional branching in the pipeline, most often associated with error conditions. These are reflected in the archive retrieval system as a column entitled "infobits". The majority of infobit states are fatal errors and either halt processing or prevent the data from being archived. However, a few infobit states are considered non-fatal but do reflect a likely error in calibration of the data. The most common of these are related to the image astrometry (bits 10, 17, and 18), and indicate that the astrometric calibration is suspect. In these cases the image contents are usually fine, as they have been correctly flat-fielded, etc. The data are therefore archived and are being released to users under the assumption that an interested astronomer could recalibrate the images.

To get the cleanest data possible, users should select data with infobits=0.

Bit

Description

0

SCAMP failed

1

WCS solution determined to be bad

2

FITS-shrinker module failed

3

JPEG-creator module failed

4

No sources found by SExtractor

8

Insufficient number of 2Mass sources in image for WCS verification

9

Insufficient number of 2Mass matches for WCS verification

10

2Mass astrometric RMSE(s) exceeded threshold

11

SExtractor before scamp failed

12

PV to SIP conversion failed

13

SCAMP terminated with exitcode=0 but had insufficient number of catalog stars

14

SCAMP terminated with exitcode=0 but had insufficient number of matches

Each Level-1 image is accompanied by a mask file. This mask file corresponds pixel-by-pixel to the science image. Each pixel contains a value where each bit encodes a specific condition. These codes are:

Bit #

Condition

0

aircraft/satellite track

1

detection by SExtractor (before flattening)

2

high dark current

3

reserved

4

noisy/hot pixel

5

ghost

6

CCD-bleed

7

rad hit

8

saturated

9

dead/bad pixel

10

not-a-number pixel

11

dirt on optics (pixel Nsigma below coarse local median)

12

halo

13

reserved

14

reserved

15

reserved

Some notes:

Because these are bit-encoded, users need to test against specific values (e.g. do not use a greater or less-than test).

Under rare conditions of exceptionally good seeing, the resulting undersampling of the beam by the large CCD pixels will result in an erroneous trigger of the radhit bit. This occurs in much of the data on the Kepler Field.

Aircraft and satellites pass over Palomar frequently, but are quite obvious.

PTF suffers substantial ghosting due to internal reflections in the optical train. An empirical algorithm maps ghosts based on bright stars from a parent catalog. While this model identifies the majority of the ghosts (which arise from a specific set of internal reflections), there are others which are not mapped at all. Further, it does not predict the complex shape of the ghosts, but instead masks an affected circular region. Ghosts most often manifest in the catalog data as distortions in object photometry, as the ghosts have hard edges which affect background estimation.